Ciesielski Arkadiusz, Skowronski Lukasz, Górecka Ewa, Kierdaszuk Jakub, Szoplik Tomasz
University of Warsaw, Faculty of Physics, Pasteura 5 str., 02-093 Warsaw, Poland.
UTP University of Science and Technology, Institute of Mathematics and Physics, Kaliskiego 7 Str. 85-796 Bydgoszcz, Poland.
Beilstein J Nanotechnol. 2018 Jan 8;9:66-76. doi: 10.3762/bjnano.9.9. eCollection 2018.
We investigated the crystallinity and optical parameters of silver layers of 10-35 nm thickness as a function 2-10 nm thick Ge wetting films deposited on SiO substrates. X-ray reflectometry (XRR) and X-ray diffraction (XRD) measurements proved that segregation of germanium into the surface of the silver film is a result of the gradient growth of silver crystals. The free energy of Ge atoms is reduced by their migration from boundaries of larger grains at the Ag/SiO interface to boundaries of smaller grains near the Ag surface. Annealing at different temperatures and various durations allowed for a controlled distribution of crystal dimensions, thus influencing the segregation rate. Furthermore, using ellipsometric and optical transmission measurements we determined the time-dependent evolution of the film structure. If stored under ambient conditions for the first week after deposition, the changes in the transmission spectra are smaller than the measurement accuracy. Over the course of the following three weeks, the segregation-induced effects result in considerably modified transmission spectra. Two months after deposition, the slope of the silver layer density profile derived from the XRR spectra was found to be inverted due to the completed segregation process, and the optical transmission spectra increased uniformly due to the roughened surfaces, corrosion of silver and ongoing recrystallization. The Raman spectra of the Ge wetted Ag films were measured immediately after deposition and ten days later and demonstrated that the Ge atoms at the Ag grain boundaries form clusters of a few atoms where the Ge-Ge bonds are still present.
我们研究了沉积在SiO衬底上厚度为2 - 10 nm的Ge湿膜对厚度为10 - 35 nm的银层的结晶度和光学参数的影响。X射线反射率（XRR）和X射线衍射（XRD）测量证明，锗在银膜表面的偏析是银晶体梯度生长的结果。Ge原子从Ag/SiO界面处较大晶粒的边界迁移到Ag表面附近较小晶粒的边界，从而降低了其自由能。在不同温度和不同持续时间下进行退火，可以控制晶体尺寸的分布，进而影响偏析速率。此外，通过椭偏测量和光学透射测量，我们确定了薄膜结构随时间的演变。如果在沉积后的第一周在环境条件下储存，透射光谱的变化小于测量精度。在接下来的三周内，偏析诱导效应导致透射光谱发生显著变化。沉积两个月后，由于偏析过程完成，从XRR光谱得出的银层密度分布曲线的斜率被发现反转，并且由于表面粗糙化、银的腐蚀和持续的再结晶，光学透射光谱均匀增加。在沉积后立即和十天后测量了Ge浸润Ag膜的拉曼光谱，结果表明Ag晶界处的Ge原子形成了几个原子的团簇，其中仍然存在Ge-Ge键。
